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J. Perelman
"Entertaining physics". Book 1.
Chapter 9. Vision one and two eyes

THRUST LINE AND OTHER DECEPTIONS OF VIEW

Drawn in Fig. 1 group of pins is not at first glance, nothing special. But pick up the book to eye level and, closing one eye, look at these lines so that the line of sight slid along them. (The eyes should be placed at the point where the continuation of these lines.) With this look you will find that the pins are not drawn on paper, and stuck it upright. Moving his head slightly to the side, you will see that the pins seem to lean in the same direction.


Fig. 1.
Place one eye (closing the other) about the point where the continuation of these lines.
You will see a number of pins, as if stuck in the paper.
At easy move picture side to side pins seem to be swinging.

This illusion is explained by the laws of perspective: lines drawn as would be designed on paper vertically protruding stuck pins, when you look at them in the manner described above.

The ability of our succumb to visual illusions should not only be considered as a lack of vision. It has its very beneficial side, which is often overlooked. The thing is, what if our eye was unable to give any deception, there would be no painting and we would be deprived of all the pleasures of fine arts. Artists use these visual impairments. “This trickery, all the beautiful art is based, wrote a brilliant scientist of the eighteenth century Euler in his famous,Letters about the different physical matters". - If we tend to judge things by the truth, it would be a dream art (i.e. art) could not take place, as if we were blind. In vain the artist had exhausted all the art on the mixture of colors; we'd say here on this Board red spot; that's blue, there's black and there's a few whitish lines; everything is on one surface, not seen it for nothing in the distance differences and could represent a single object. What would the picture nor was written, so it seemed to us, as the letter... When this perfection is not whether we would regrets, being deprived of the pleasure that brings us daily so pleasant and useful arts?”.

Optical illusions are a lot, you can fill a whole album of various examples of such illusions. Many of them well known, others are less familiar. Here is some more interesting examples of optical illusions from a number of less well-known. Particularly spectacular illusions Fig. 2 and 3 with lines on the mesh background: eyes positively refuses to believe that the letters in Fig. 2 put right. Even harder to believe that in Fig. 43 before us is not a spiral. Have to convince myself that the immediate challenge: putting a pencil on one of the branches of the imaginary spiral, circle arcs, not approaching and not away from the center.


Fig. 2. Letters delivered right.


Fig. 3. Curves of this figure seem spiral; however, it is a circle, what is easy to verify, leading them pointed match.

Similarly, only with the help of a compass, we can ensure that in Fig. 4 direct AC no shorter than AB.


Fig. 4. The distances AB and AC are equal, although the first seems more.

The essence of the other illusions generated by figures 5, 6, 7, 8, explained in the captions under them. To what extent strong illusion Fig. 7, shows the following curious story: publisher of one of the previous editions of my book, getting from zincography impression of the cliche, considered cliche unfinished and was already prepared to return it to the shop to be cleaned off the grey spots at the intersection of the white stripes when I accidentally entered the room, explained to him what was the matter.


Fig. 5. Oblique line crossing strips seems to be broken.


Fig. 6. White and black squares are equal, as well as circles.


Fig. 7. At the intersection of the white stripes of this figure appear and disappear, as if flashing, grayish square spots. In fact, strips completely white along the entire length, it is easily seen, by closing the paper adjacent rows of black squares. This is a consequence of contrasts.


Fig. 8. At the intersection of black bands appear grayish spots.

Entertaining physics J. Perelman

 




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